1. Field of the Invention
This invention relates to an axial piston machine, such as a swashplate machine, with a cylinder drum that is mounted so that it can rotate around an axis of rotation. The cylinder drum is provided with cylinder bores, in each of which a piston is mounted so that it can be displaced longitudinally. The cylinder drum is axially supported on a control surface that is affixed to the casing, on which control surface an inlet connection and an outlet connection are provided. The cylinder bores can each be brought into communication with the control surface by a connecting channel.
2. Technical Considerations
A generic axial piston machine utilizing a swashplate design is described in DE 43 40 061 A1, herein incorporated by reference. On axial piston machines of this type, a gap is necessary between the rotating cylinder drum and the control surface that is affixed to the casing. In the control surface, there are kidney-shaped control channels which form an inlet connection and an outlet connection of the axial piston machine. At the gap, a hydrostatic lubricating film is provided to reduce the friction between the hydrostatic friction bearing fouled by the cylinder drum and the control surface.
The cylinder drum is pressed toward the control surface by a piston force. This pressing piston force is produced by the pressure present in the cylinder bore and a pressurized surface which is formed because the cross-section of the connecting channel is smaller than the cross-section of the cylinder bore. This pressing piston force counteracts a hydrostatic compressive force which is present in the gap between the cylinder drum and the control surface. The hydrostatic compression force is formed from the pressure present in the gap and a sealing web that is formed on the end surface of the cylinder drum that faces the control surface.
The excess of force between the pressing piston force and the relieving hydrostatic compression force must thereby be designed so that, on one hand, when the gap width increases, a lifting of the cylinder drum and thus a higher leakage flow at the gap can be prevented and, on the other hand, so that excessive friction forces do not occur between the cylinder drum and the control surface and cause wear when the gap width is too small.
However, particularly when the cylinder bore is reversed from the inlet connection to the outlet connection at top and bottom dead center (and thus reversed from low pressure to high pressure or from high pressure to low pressure), the hydrostatic pressure force is subjected to disturbance effects which, in practice, are counteracted by an increase in the piston force applied and thus a high transfer of force between the pressing piston force and the relieving compressive force. This high transmission of force, however, leads to an increase of friction between the cylinder drum and control surface and thus a reduction in efficiency as well as an increase in the wear of the axial piston machine. Therefore, it is an object of this invention to provide a hydrostatic axial piston machine of the general type described above but which is characterized by increased efficiency and reduced wear.